HP 9816

This machine was purchased 3 or 4 years ago from a local enthusiast who simply didn’t have time to work on it. It also included a couple of HPIB cables, a 9131 and a 9133 (I think, will need to confirm). No software or documentation was included.

After figuring out how the machine was supposed to work, I booted it up. Well, I tried to boot it up but it wouldn’t start. After cycling the power switch, the fan would finally come on and after a couple of additional cycles the screen would come up and it would eventually boot. It has a small amount of bad ram in one of the 256k expansion boards and 1 of the 3 3-1/2″ floppy drives does not work properly. However the hard drive has some information and is bootable but I have the same boot problems each time I try to bring it up.

Recently, I finally had time to open up the power supply and found 5 RIFAs. Two of the RIFAs are physically larger packages and were showing signs of failure. I don’t expect this to help the boot issues but will make me feel a bit safer while troubleshooting the machine. As of 6/18/2022 now have the RIFA caps ordered and expect them soon. Hopefully will have machine to the point of troubleshooting.

RIFA caps arrived 2022-06-22. Installed RIFAs on 2022-06-23 and tested, RIFAs work fine but power supply problem still exists. When powered up, the power supply generates 0.55 V on +5 V rail and +/- 0.15 on the +/-15 V rails. Now studying prints trying to understand which power supply component might cause this behavior. I might pick up another power supply with similar ratings and try it to see if it a problem directly with the 9816 power supply or some other issue.

Photos and Info

If you need more details about a specific component I can pull the power supply again, it’s actually a pretty easy process. Tony Duell’s schematics are terrific but he doesn’t necessarily have all components documented completed.

Note, if you’re replacing RIFA caps (which is very highly recommended due to the fact that they will probably blow after 30 years), make sure you observe the X and Y type of the capacitor. This is pretty important and I would take the time to understand the difference and what is available. There are lots of good articles through DuckDuckGo (or Google if you must). Apple II power supplies have RIFA issues also.